This invention consists of two distinct themes:
a buckling slender column used as a spring with nearly constant force; and PA1 a printed circuit array of springs, particularly non-cantilever or non-planar springs.
In some current electromechanical applications there is a requirement for an array of springs which can exert near-constant force over a considerable range of deflection. In varying applications a single spring element may be utilized. In other representative applications the springs may be closely spaced in an array consisting of 2 rows by 2 columns for a total of 4 spring elements, up to and possibly exceeding 15 rows by 15 columns, for a total of 225 spring elements. The requirements also provide that the end product be simple in design, easily manufacturable, and possess the desired non-linear properties.
This invention thus provides a printed circuit of springs which integrates a dense array of many functionally distinct springs into one thin metal sheet. The sheet is folded so individual springs protrude perpendicularly from the sheet. An individual spring has multiple columns which bend by buckling during deflection (compression). For a significant range of deflection, the spring force is nearly constant, and there is minimal lateral sideways force and displacement.
A dense array of numerous discrete springs according to previous technology imposes a penalty in complexity, fabrication, assembly and cost. By contrast, a goal of this present invention is to improve simplicity, fabrication, assembly and cost.
It is known that a collimated beam axially loaded will initially be stiff until sufficient lateral deflection of some portion of the beam occurs to cause the member to "buckle", creating a drastic change in deflection per additionally applied load. Building upon that principle, it has been discovered that two centrally joined opposing flat beams, having a slightly outward bowed cross section could exert a nearly constant axial force over a relatively large range of displacements, and the coupling of the beams allows the opposing forces to cancel any lateral displacement of the central axis, but act additively to exert a constant force against the perpendicularly applied load.
It was discovered that variations in the basic parameters of thickness, material type, and width of legs will alter the spring rate. Varying height and selectively removing material to balance internal stresses upon deflection produces an extended near-constant-force band.
Testing of this invention has shown that the unitary array design greatly improves manufacturability over prior art designs utilizing discrete components such as a series of coil springs, and the unitary design also offers a substantially higher spring rate than would a comparably sized cantilever spring occupying the same volume.
Standard coil and cantilever springs produce a linear or extra-linear increase in force with deflection while the opposite--a sub-linear increase in force with deflection--has been found to be true for the buckling beam type spring of the present invention.
Although the spring array was designed to serve a specific purpose, the versatility of design and performance characteristics suggest numerous application; some using existing designs and others using modified designs .